Stanford researchers say climate change affects where plants grow

A lizard is almost invisible, camouflaged in a bush. A bumblebee flits about and pauses on one of the plant’s flowers. An ant descends a stem, delivering food to her brothers.

What kind of lives would the lizard, bee, and ant lead without this plant?

It’s not a question we ask ourselves often. At a recent seminar, Stanford University ecologist Dr. Terry Root reminded her audience of the myriad interactions between living creatures in their environments – as well as the potentially devastating effects of sudden alterations to those environments. With mounting evidence in support of global warming, Root and a team of Stanford researchers have been exploring the effects of changes in climate on living things. More specifically, they’re trying to deduce the impact of climate on California plants over the past hundred years.

Animals and plants alike respond in a variety of ways to shifts in their environment. In response to an increase in global temperature, for example, over time a population of a particular species might shift its geographic range towards traditionally cooler locations, i.e. towards the poles or up in elevation. Root discussed these and other responses of organisms to their environments at the April meeting of the “Sustainability and Resource Management” seminar series, held weekly over the spring academic quarter at Stanford and devoted to discussing issues such as climate stability and sustainable energy approaches.

To discover how California plant distributions have changed over time, the Stanford team is using a comprehensive dataset: museum specimens of a large number of California plants. Since the mid 1800’s and until the present day, these plants have been collected by a variety of individuals, from the famous naturalist John Muir to amateur botanists, says William Anderegg, a Stanford graduate student in biology involved in the project. When and where the plants were picked can be used to assess how the locations of the plants themselves have changed over time.

But analyzing this dataset is not straightforward. Dr. Scott Loarie, a Stanford ecologist and climate scientist who is not involved with the project, said, “…museums have all this incredible data over this historical period, but no model for how the data is collected.” For instance, plant collectors might frequently visit and sample plants in a particular area of California in one decade, but not in others, for reasons having nothing to do with the plants’ distributions.

This January, Shawn Crimmins and colleagues at the University of Montana published a similar study of California plant species movements, analyzing a part of the dataset used by the Stanford team. The group discovered that plants moved down, rather than up, in elevation, driven by water availability. However, Anderegg claims that the group did not correctly account for differences in how plants have been collected over time, and that “they could have … gotten a completely false trend due only to sampling.”

To address that possibility, the Stanford team collaborated with Adam Wolf, a postdoctoral associate at Princeton University, to develop a new statistical method to obtain accurate plant location information that accounts for biases in where and when plants were sampled. Using their new method, the team is attempting to better understand the movements of California plant species. One preliminary finding is that the distribution of plants in the Mojave Desert are moving up in elevation over time, in accord with the increasing temperature hypothesis. The group hopes to find why species in other locations are moving more, less, or not at all.

The next challenge will be to discover which and how many plant species distribution shifts are driven by changes in climate, Anderegg said. Using detailed climate data collected since the 1800’s, the team can learn whether plant location changes are linked to rainfall, temperature, drought, or random variation. Understanding the factors that drive changes in plant species distributions, and whether humans have contributed to those factors, can help to elucidate the impacts of human activities on other living things.

Loarie said the group’s aim to “look at the past … to understand these processes is extremely valuable.” This work also has important implications in planning for climate change. Details about how species have been changing could help to inform future decisions regarding conservation and preservation of species that may be in danger.

It all ties back into the broader research task on Root’s agenda: learning about species interactions to better understand the full impact of climate change. Think back to the plant, bee, ant, and lizard, all intertwined in their environment. A change in the location of the plant could have profound consequences on the others. Root believes that with further research, we can prepare ourselves, and other species, for the shifts and disruptions that our actions may have already set in motion.

“There is hope,” she said.

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